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Montana officials are warning that if the Supreme Court rules in the D.C. gun ban case that the right to keep and bear arms protects only state-run militias like the National Guard, then the federal government will have breached Montana’s statehood contract.

Nobody is raising flags for the Republic of Montana, but nobody is kidding, either. So far, 39 elected Montana officials have signed a resolution declaring that a court ruling of the Second Amendment is a right of states and not of individuals would violate Montana’s compact.

“The U.S. would do well to keep its contractual promise to the states that the Second Amendment secures an individual right now as it did upon execution of the statehood contract,” Montana Secretary of State Brad Johnson said in a Feb. 15 letter to The Washington Times.

The resolution also was signed by Rep. Denny Rehberg, Montana’s lone Republican congressman, and state Sen. Roy Brown, who is running to unseat Gov. Brian Schweitzer, a Democrat.

The dispute goes back more than a century. Back in 1889, the settlers of the Montana territory struck a deal with the federal government: They agreed to join the union, and the government agreed that individuals had the right to bear arms.

That has worked fine for the past 118 years, but the Supreme Court is expected next month to hear oral argument in District of Columbia v. Heller, the appeal of a federal court decision striking down the District’s gun-ownership ban on Second Amendment grounds.

The high court has not issued a broad ruling on Second Amendment law in almost 70 years, including the key question of whether it provides an individual right, like speech and jury trial, or a “collective right” held by state governments. Many constitutional scholars, both liberal and conservative, say this case gives the justices an opportunity to rule on that matter.

The Montana statehood contract, which was preserved as Article I of the state constitution, specifies gun ownership as an individual right: “The right of any person to keep or bear arms … shall not be called in question.”

“There was a promise made to Montana that the right to bear arms was an individual right,” said Gary Marbut, president of the Montana Shooting Sports Association and the author of a book on Montana gun law.

What’s more, he said, a “collective-rights” interpretation would have been impossible because Montana had no state-run militia in the 1880s.

“It’s pretty disingenuous as an argument,” said Mr. Marbut. “At the time, they had no image of what a National Guard was. But history and logic don’t always prevail in these matters.”

Not all firearms advocates support the logic of the Montana resolution. Dave Kopel, a lawyer who runs the Independence Institute’s Second Amendment Project in Golden, Colo., said the argument doesn’t pass legal muster.

“Of course the historical evidence is unanimous that in 1889, the Second Amendment was considered to be an individual right comparable to the individual right of free speech,” Mr. Kopel said in an e-mail. “However, the Montana Constitution’s Compact Article does not prove that Montana entered the union contingent on the existence of a personal right to keep and bear arms in the U.S. Constitution.”

At the same time, Mr. Kopel calls the collective-rights argument “totally implausible on every ground, other than desire of the contemporary gun prohibition movement to nullify part of the Constitution.”